open iftop for each (cfg’d) network interface:

for i in $(ifconfig -lu); do if ifconfig $i | fgrep -v 'inet 127.' | grep -q "inet [0-9]"; then echo $i; fi; done | while read intfc; do osascript -e "tell application \"terminal\" to do script \"sudo iftop -i $intfc\""; done

(Mac; could be adapted)